Ramon Frederick - Academia.edu (original) (raw)
Papers by Ramon Frederick
International Journal of Heat and Fluid Flow, Apr 1, 1995
Natural convection in the central microcavities of vertical, finned cavities of very high aspect ... more Natural convection in the central microcavities of vertical, finned cavities of very high aspect ratios were numerically investigated using a spacewise periodical approach. When equally spaced fins are located on both active walls (problem b), different circulation rates are found in two consecutive microcavities. The average Nusselt number in a region comprising two consecutive microcavities is higher than the one
International Journal of Heat and Mass Transfer, Feb 1, 1994
A full 3-D numerical study is reported on natural convection of air in six heated-from-below para... more A full 3-D numerical study is reported on natural convection of air in six heated-from-below parallelepipedic enclosures. A supercritical Rayleigh number (Ru = 8 x 103), was used in order to track the evolution of convective structures as a function of the enctosure's aspect ratio (A) only. The six situations (1 < A < 5) exhibit a characteristic toroidal flow pattern which can be seen, at the lowest aspect ratio, as a unicellular structure which evolves to a multicellular combination of concentric roll-cells at higher aspect ratios. The transition from one convective structure to another has the features of a flow bifurcation controlled by A. The overall Nusselt number changed continuously when the aspect ratio was increased. At the lowest aspect ratios the change was significant, but further increments in A did not produce important variations in this parameter, in the range of aspect ratios studied.
International Journal of Heat and Fluid Flow, Apr 1, 2007
Three-dimensional natural convection of air in a cubical enclosure with a fin on the hot wall is ... more Three-dimensional natural convection of air in a cubical enclosure with a fin on the hot wall is numerically investigated for Rayleigh numbers of 10 3-10 6. The fin, with a thickness of 1/10 of the cavity side, is placed horizontally on the hot wall. The solid to fluid thermal conductivity ratio (R k) and the fin width are varied. Because the fin is shorter than the cavity side, the cold flow sweeps the lower fin face and the hot wall at the clearances between the fin sides and the lateral walls, where high vertical velocities are reached. The fin inhibits the frontal and lateral access of fluid to the upper fin face, especially at low Rayleigh numbers. Low values of R k cause heat transfer reductions. The contribution of the fin faces increases at high R k causing heat transfer enhancements above 20%, which exceed the ones obtained in most two-dimensional studies. In the range of Ra from 10 5 to 10 6 , maximum heat transfer rates are found for dimensionless fin widths of 0.6 and 0.8 respectively. It is concluded that for 10 5 6 Ra 6 10 6 a fin of partial width is more effective in promoting heat transfer than a fin of full width.
Proceeding of 5-6th Thermal and Fluids Engineering Conference (TFEC), 2021
Proceeding of 3rd Thermal and Fluids Engineering Conference (TFEC), 2018
Latin American Applied Research, 1989
WIT Transactions on Engineering Sciences, 2008
Flow patterns and heat transfer in a square cavity with perfectly conducting horizontal walls are... more Flow patterns and heat transfer in a square cavity with perfectly conducting horizontal walls are described by direct simulation for Rayleigh numbers of 10 6-10 9. The code uses second order time and space discretisations and non-uniform grids. For Ra = 10 6 or less a steady final state is found. Periodic characteristics are obtained at Ra = 10 7 , and non periodic behaviour is found at higher Ra. Time averaged wall and mid plane Nusselt numbers (not previously known for this case) are reported and correlated. Their oscillation frequencies are determined to characterize the regime. The mid plane Nusselt number, mid Nu , always exceeds wall Nusselt numbers. mid Nu represents the total heat moved by the cavity under the perfectly conducting condition. At Rayleigh numbers from 10 8 onwards, mid Nu exceeds the corresponding value for the adiabatic problem.
WIT Transactions on Engineering Sciences, 2010
Heat transfer enhancement with highly conductive, thin vertical fins attached to the hot wall of ... more Heat transfer enhancement with highly conductive, thin vertical fins attached to the hot wall of a differentially heated cubical enclosure is numerically investigated. Two such fins attached to the hot wall were found to promote heat transfer enhancements of over 40% with respect to the unfinned case at Ra = 10 5-10 7. This is one of the highest enhancements found to date in cavities of low aspect ratio. At a Rayleigh number of 10 8 , enhancements were lower, suggesting that this Rayleigh number marks the upper utilization limit of fins in enclosures to promote heat transfer. Results show that for further heat transfer optimization, sensitivity to variables as the fin thickness and length should be studied.
WIT Transactions on Engineering Sciences, 2012
Two dimensional transient modelling of the flow and heat transfer in an idealized Trombe wall sys... more Two dimensional transient modelling of the flow and heat transfer in an idealized Trombe wall system was performed for a fixed set of physical dimensions. The governing equations were solved using multiphysics software. Buoyancy and thermal accumulation in a brick wall are the main effects considered. During operation, the solid and fluid temperatures constantly increase, while circulation flow rates, which are significant from the start, show a slow decrease. The room is heated by the parallel mechanisms of buoyancy flow from the collector space and directly by the hot wall, but the latter effect becomes progressively more important. Heat losses through the glazed surfaces of room and collector are of similar magnitude. However, when the wall clearances are closed the collector loss shows an important increase. The role of the typical Trombe wall circulation in the control of heat losses is discussed.
Numerical Heat Transfer, Part A: Applications, 1991
Numerical solutions, based on the streamfunction-vorticity formulation, were obtained for two-dim... more Numerical solutions, based on the streamfunction-vorticity formulation, were obtained for two-dimensional flow of air in a differentially heated, slender cavity with conducting fins on the cold wall, for Rayleigh numbers of 10-10, angles of inclination of 45° and 90°, overall aspect ratios of 20 and ∞, and microcavity aspect ratios (A) of 20-0.25. As A was decreased from a value
Numerical Heat Transfer, Part A: Applications, 2002
Natural convection in a cubical enclosure with a hot source centered on a vertical wall and with ... more Natural convection in a cubical enclosure with a hot source centered on a vertical wall and with an adjacent, fully cooled vertical wall was numerically investigated for Rayleigh numbers ( Ras ) of 10 3 - 4 2 10 6 . At Ra < 10 5 the heat transfer strongly depends on the hot sector side and its dependence on Ra is weak. Opposite characteristics occur at very high Ra , and there is a long transition between these two regimes. This behavior is caused by a mixing pattern, which, at low Ra , is similar to the one found in side heated cavities, whereas at high Rayleigh numbers lateral mixing is dominant.
International Journal of Heat and Mass Transfer, 2001
... studied flow structures, thermal fields, and stability conditions in vertical and inclined cu... more ... studied flow structures, thermal fields, and stability conditions in vertical and inclined cubicalenclosures ... In this paper, we study the steady-state, laminar natural convection in a cubicalenclosure ... 4(b), where heat transfer is essentially by convection, with thermal stratification and ...
International Journal of Heat and Mass Transfer, 1989
Natural convection of air in square cavities with half-active and half-insulated vertical walls i... more Natural convection of air in square cavities with half-active and half-insulated vertical walls is numerically investigated for Rayleigh numbers of 103-10'. This problem is related to applications in solar collection and cooling of electronic components. Five different relative positions of the active zones are considered. While circulation depends strongly on the total exit length downstream of the active zones, heat transfer depends less on this parameter. Significant conduction effects occur even at a Rayleigh number of 10'. Expressions for average Nusselt number in the five situations and hints on how to generalize heat transfer results to intermediate cases are given.
International Journal of Heat and Mass Transfer, 1989
Natural convection in an inclined differentially heated square enclosure containing internally he... more Natural convection in an inclined differentially heated square enclosure containing internally heated fluid has been investigated numerically using the Galerkin finite element method. The horizontal walls are adiabatic, while the side walls are isothermal but kept at different temperatures. Flow and heat transfer characteristics through isotherms, streamlines and average Nusselt numbers have been presented for the external Rayleigh number 10 3 to 10 6 , internal Rayleigh number 10 5 to 10 8 and inclination angles 0º to 30º. The obtained computational results indicate that the strength of the convective currents depends on the internal energy. Heat removal rate is optimized at zero inclination angle for relatively weak external heating mode for all values of internal energy.
International Journal of Heat and Fluid Flow, 1995
Natural convection in the central microcavities of vertical, finned cavities of very high aspect ... more Natural convection in the central microcavities of vertical, finned cavities of very high aspect ratios were numerically investigated using a spacewise periodical approach. When equally spaced fins are located on both active walls (problem b), different circulation rates are found in two consecutive microcavities. The average Nusselt number in a region comprising two consecutive microcavities is higher than the one
International Communications in Heat and Mass Transfer, 1994
Experimental simulation of the external forced convection on the outside of grape packages was pe... more Experimental simulation of the external forced convection on the outside of grape packages was performed. Average heat transfer coefficients for air flow around such containers were found to range from 8 to 13.4 W/(m2K). A physical description of the convective process was formulated on the basis of data obtained in three types of experiment. Expressions for the average heat transfer coefficient from single packages in air flow were proposed.
International Communications in Heat and Mass Transfer, 1989
Natural convection in a square cavity with a conducting partition on its hot wall and with perfec... more Natural convection in a square cavity with a conducting partition on its hot wall and with perfectly conducting horizontal walls is numerically studied. The divider length and the divider-to-fluid thermal conductivity ratio (Rk) are varied. For low values of Rk, reductions in heat transfer relative to the undivided cavity are obtained, especially for Rayleigh numbers of 104–105. This reduction is more significant when long dividers are used.
International Communications in Heat and Mass Transfer, 1997
Natural convection of air in a cubical enclosure of edge L with a cold wall covering one of the v... more Natural convection of air in a cubical enclosure of edge L with a cold wall covering one of the vertical surfaces and a hot square sector of side s centred on the opposite wall is considered The overall heat transfer shows similar dependancies to the case of side heated cavities for s/L > 0.5. llie main circulation cell is similar to that in the test problem, but becomes progressively distorted by expansions, contractions and secondary loops at high Ra and at low values of s/L It is shown that the average fluid temperature can be used as a criterion for transition to a convective regime.
International Communications in Heat and Mass Transfer, 1999
A numerical study of two dimensional natural convection of air in rectangular, differentially hea... more A numerical study of two dimensional natural convection of air in rectangular, differentially heated cavities was conducted. For three Rayleigh numbers the aspect ratio S was varied. It was found that heat transfer between the active walls has a maximum at each Rayleigh number, which is located at values of S between 1 and 2. The aspect ratio for which the maximum heat transfer occurs is determined by the process of transition from a shallow cavity regime to a slender cavity regime.
International Communications in Heat and Mass Transfer, 2004
International Journal of Heat and Fluid Flow, Apr 1, 1995
Natural convection in the central microcavities of vertical, finned cavities of very high aspect ... more Natural convection in the central microcavities of vertical, finned cavities of very high aspect ratios were numerically investigated using a spacewise periodical approach. When equally spaced fins are located on both active walls (problem b), different circulation rates are found in two consecutive microcavities. The average Nusselt number in a region comprising two consecutive microcavities is higher than the one
International Journal of Heat and Mass Transfer, Feb 1, 1994
A full 3-D numerical study is reported on natural convection of air in six heated-from-below para... more A full 3-D numerical study is reported on natural convection of air in six heated-from-below parallelepipedic enclosures. A supercritical Rayleigh number (Ru = 8 x 103), was used in order to track the evolution of convective structures as a function of the enctosure's aspect ratio (A) only. The six situations (1 < A < 5) exhibit a characteristic toroidal flow pattern which can be seen, at the lowest aspect ratio, as a unicellular structure which evolves to a multicellular combination of concentric roll-cells at higher aspect ratios. The transition from one convective structure to another has the features of a flow bifurcation controlled by A. The overall Nusselt number changed continuously when the aspect ratio was increased. At the lowest aspect ratios the change was significant, but further increments in A did not produce important variations in this parameter, in the range of aspect ratios studied.
International Journal of Heat and Fluid Flow, Apr 1, 2007
Three-dimensional natural convection of air in a cubical enclosure with a fin on the hot wall is ... more Three-dimensional natural convection of air in a cubical enclosure with a fin on the hot wall is numerically investigated for Rayleigh numbers of 10 3-10 6. The fin, with a thickness of 1/10 of the cavity side, is placed horizontally on the hot wall. The solid to fluid thermal conductivity ratio (R k) and the fin width are varied. Because the fin is shorter than the cavity side, the cold flow sweeps the lower fin face and the hot wall at the clearances between the fin sides and the lateral walls, where high vertical velocities are reached. The fin inhibits the frontal and lateral access of fluid to the upper fin face, especially at low Rayleigh numbers. Low values of R k cause heat transfer reductions. The contribution of the fin faces increases at high R k causing heat transfer enhancements above 20%, which exceed the ones obtained in most two-dimensional studies. In the range of Ra from 10 5 to 10 6 , maximum heat transfer rates are found for dimensionless fin widths of 0.6 and 0.8 respectively. It is concluded that for 10 5 6 Ra 6 10 6 a fin of partial width is more effective in promoting heat transfer than a fin of full width.
Proceeding of 5-6th Thermal and Fluids Engineering Conference (TFEC), 2021
Proceeding of 3rd Thermal and Fluids Engineering Conference (TFEC), 2018
Latin American Applied Research, 1989
WIT Transactions on Engineering Sciences, 2008
Flow patterns and heat transfer in a square cavity with perfectly conducting horizontal walls are... more Flow patterns and heat transfer in a square cavity with perfectly conducting horizontal walls are described by direct simulation for Rayleigh numbers of 10 6-10 9. The code uses second order time and space discretisations and non-uniform grids. For Ra = 10 6 or less a steady final state is found. Periodic characteristics are obtained at Ra = 10 7 , and non periodic behaviour is found at higher Ra. Time averaged wall and mid plane Nusselt numbers (not previously known for this case) are reported and correlated. Their oscillation frequencies are determined to characterize the regime. The mid plane Nusselt number, mid Nu , always exceeds wall Nusselt numbers. mid Nu represents the total heat moved by the cavity under the perfectly conducting condition. At Rayleigh numbers from 10 8 onwards, mid Nu exceeds the corresponding value for the adiabatic problem.
WIT Transactions on Engineering Sciences, 2010
Heat transfer enhancement with highly conductive, thin vertical fins attached to the hot wall of ... more Heat transfer enhancement with highly conductive, thin vertical fins attached to the hot wall of a differentially heated cubical enclosure is numerically investigated. Two such fins attached to the hot wall were found to promote heat transfer enhancements of over 40% with respect to the unfinned case at Ra = 10 5-10 7. This is one of the highest enhancements found to date in cavities of low aspect ratio. At a Rayleigh number of 10 8 , enhancements were lower, suggesting that this Rayleigh number marks the upper utilization limit of fins in enclosures to promote heat transfer. Results show that for further heat transfer optimization, sensitivity to variables as the fin thickness and length should be studied.
WIT Transactions on Engineering Sciences, 2012
Two dimensional transient modelling of the flow and heat transfer in an idealized Trombe wall sys... more Two dimensional transient modelling of the flow and heat transfer in an idealized Trombe wall system was performed for a fixed set of physical dimensions. The governing equations were solved using multiphysics software. Buoyancy and thermal accumulation in a brick wall are the main effects considered. During operation, the solid and fluid temperatures constantly increase, while circulation flow rates, which are significant from the start, show a slow decrease. The room is heated by the parallel mechanisms of buoyancy flow from the collector space and directly by the hot wall, but the latter effect becomes progressively more important. Heat losses through the glazed surfaces of room and collector are of similar magnitude. However, when the wall clearances are closed the collector loss shows an important increase. The role of the typical Trombe wall circulation in the control of heat losses is discussed.
Numerical Heat Transfer, Part A: Applications, 1991
Numerical solutions, based on the streamfunction-vorticity formulation, were obtained for two-dim... more Numerical solutions, based on the streamfunction-vorticity formulation, were obtained for two-dimensional flow of air in a differentially heated, slender cavity with conducting fins on the cold wall, for Rayleigh numbers of 10-10, angles of inclination of 45° and 90°, overall aspect ratios of 20 and ∞, and microcavity aspect ratios (A) of 20-0.25. As A was decreased from a value
Numerical Heat Transfer, Part A: Applications, 2002
Natural convection in a cubical enclosure with a hot source centered on a vertical wall and with ... more Natural convection in a cubical enclosure with a hot source centered on a vertical wall and with an adjacent, fully cooled vertical wall was numerically investigated for Rayleigh numbers ( Ras ) of 10 3 - 4 2 10 6 . At Ra < 10 5 the heat transfer strongly depends on the hot sector side and its dependence on Ra is weak. Opposite characteristics occur at very high Ra , and there is a long transition between these two regimes. This behavior is caused by a mixing pattern, which, at low Ra , is similar to the one found in side heated cavities, whereas at high Rayleigh numbers lateral mixing is dominant.
International Journal of Heat and Mass Transfer, 2001
... studied flow structures, thermal fields, and stability conditions in vertical and inclined cu... more ... studied flow structures, thermal fields, and stability conditions in vertical and inclined cubicalenclosures ... In this paper, we study the steady-state, laminar natural convection in a cubicalenclosure ... 4(b), where heat transfer is essentially by convection, with thermal stratification and ...
International Journal of Heat and Mass Transfer, 1989
Natural convection of air in square cavities with half-active and half-insulated vertical walls i... more Natural convection of air in square cavities with half-active and half-insulated vertical walls is numerically investigated for Rayleigh numbers of 103-10'. This problem is related to applications in solar collection and cooling of electronic components. Five different relative positions of the active zones are considered. While circulation depends strongly on the total exit length downstream of the active zones, heat transfer depends less on this parameter. Significant conduction effects occur even at a Rayleigh number of 10'. Expressions for average Nusselt number in the five situations and hints on how to generalize heat transfer results to intermediate cases are given.
International Journal of Heat and Mass Transfer, 1989
Natural convection in an inclined differentially heated square enclosure containing internally he... more Natural convection in an inclined differentially heated square enclosure containing internally heated fluid has been investigated numerically using the Galerkin finite element method. The horizontal walls are adiabatic, while the side walls are isothermal but kept at different temperatures. Flow and heat transfer characteristics through isotherms, streamlines and average Nusselt numbers have been presented for the external Rayleigh number 10 3 to 10 6 , internal Rayleigh number 10 5 to 10 8 and inclination angles 0º to 30º. The obtained computational results indicate that the strength of the convective currents depends on the internal energy. Heat removal rate is optimized at zero inclination angle for relatively weak external heating mode for all values of internal energy.
International Journal of Heat and Fluid Flow, 1995
Natural convection in the central microcavities of vertical, finned cavities of very high aspect ... more Natural convection in the central microcavities of vertical, finned cavities of very high aspect ratios were numerically investigated using a spacewise periodical approach. When equally spaced fins are located on both active walls (problem b), different circulation rates are found in two consecutive microcavities. The average Nusselt number in a region comprising two consecutive microcavities is higher than the one
International Communications in Heat and Mass Transfer, 1994
Experimental simulation of the external forced convection on the outside of grape packages was pe... more Experimental simulation of the external forced convection on the outside of grape packages was performed. Average heat transfer coefficients for air flow around such containers were found to range from 8 to 13.4 W/(m2K). A physical description of the convective process was formulated on the basis of data obtained in three types of experiment. Expressions for the average heat transfer coefficient from single packages in air flow were proposed.
International Communications in Heat and Mass Transfer, 1989
Natural convection in a square cavity with a conducting partition on its hot wall and with perfec... more Natural convection in a square cavity with a conducting partition on its hot wall and with perfectly conducting horizontal walls is numerically studied. The divider length and the divider-to-fluid thermal conductivity ratio (Rk) are varied. For low values of Rk, reductions in heat transfer relative to the undivided cavity are obtained, especially for Rayleigh numbers of 104–105. This reduction is more significant when long dividers are used.
International Communications in Heat and Mass Transfer, 1997
Natural convection of air in a cubical enclosure of edge L with a cold wall covering one of the v... more Natural convection of air in a cubical enclosure of edge L with a cold wall covering one of the vertical surfaces and a hot square sector of side s centred on the opposite wall is considered The overall heat transfer shows similar dependancies to the case of side heated cavities for s/L > 0.5. llie main circulation cell is similar to that in the test problem, but becomes progressively distorted by expansions, contractions and secondary loops at high Ra and at low values of s/L It is shown that the average fluid temperature can be used as a criterion for transition to a convective regime.
International Communications in Heat and Mass Transfer, 1999
A numerical study of two dimensional natural convection of air in rectangular, differentially hea... more A numerical study of two dimensional natural convection of air in rectangular, differentially heated cavities was conducted. For three Rayleigh numbers the aspect ratio S was varied. It was found that heat transfer between the active walls has a maximum at each Rayleigh number, which is located at values of S between 1 and 2. The aspect ratio for which the maximum heat transfer occurs is determined by the process of transition from a shallow cavity regime to a slender cavity regime.
International Communications in Heat and Mass Transfer, 2004